(1) Field of the Invention
The invention relates generally to wood cutting equipment, and more particularly to automated feeding of fixed arbor gang rip saws and a method for minimizing scrap wood through optimizing the area of wood that is cut.
(2) Description of the Related Art
In operations involving the cutting of wood in, for example, sawmills, or in processing for the production of furniture, several considerations are taken into account in cutting wood economically. These include the speed with which the wood is fed to gang saws, the safety of the workers who are responsible for feeding the wood into the saws, and the number of pieces into which each board can be cut.
Another important consideration is the optimal way in which an incoming piece of wood stock of irregular shape can be cut to reduce waste. Typically, a log is first cut lengthwise along a number of parallel, axial planes to yield a number of irregularly shaped planks sometimes referred to as "cants". Cants cut from the same log all have the same length. However, the height (or width, when later placed flat on its broad side) of each cant will vary depending upon where on the diameter of the log the cut is made. Furthermore, the thickness of each plank will be determined by the spacing of saw blades, if the log is cut in a gang saw. Usually, when cutting planks or cants from the same log, the blades are set equidistant from each other so that the resulting planks all have the same thickness. While the thickness of each cant is therefore the same in this arrangement of the blades, the height of each cant, will vary depending upon the particular section of the log that is cut. For example, cants which are cut from sections close to the center of the log will be higher than those cut near the edges. Moreover, the cants will generally taper in one direction corresponding to the lessening diameter of the tree toward its top.
In the prior art, methods have been disclosed for maximizing the yield of wood stock. As disclosed in U.S. Pat. No. 4,468,992 (McGeehee), this means maximizing the total board feet of lumber derived from each log, although it may mean recovering a maximum number of boards of a certain length or having some other characteristic which makes them particularly valuable. Regardless of the particular optimization criteria employed, it is not obvious from examining an unfinished cant how to optimize the cutting of the cant into individual boards. For that reason McGeehee proposes an apparatus and a method where a cant is sawed simultaneously into a plurality of individual boards having optimum dimensions.
During a sawing operation, accurate alignment of planks or cants is important. One method of aligning is illustrated in FIGS. 1a and 1b, in which alignment pins are used in a conveyor system. The system consists of an infeed conveyer 20 at one end and an outfeed conveyer 60 with a sawing table 40 in between. Both conveyers are conventional chain conveyers comprising a plurality of individual chains 22 and 62, respectively, and carrying with them lugs 21 and 61 to lug along cants 10 and 10' as shown in FIG. 1a. Chains 22 are driven synchronously so that advancing lugs 21 remain transversely aligned and cant 10 is advanced in normal direction to its elongate axis, i.e., in direction 11 to the right in FIGS. 1a and 1b. Cant 10 is next transferred on to an optical scanning table 30 by means of infeed transfer arms 31. An optical system (not shown on table 30) comprising light sources, light detectors and reflectors is then used to gather information to determine the optimum orientation of cant 10.
The means of moving and at the same time aligning cant 10 in an apparatus of prior art such as shown in FIGS. 1a and 1b can be quite complicated. Thus, each advancing rod 23 is fitted with a retractable pin 24 at its forward end. As described in U.S. Pat. No. 4,468,992, in its raised position, pin 24 projects upward through a slot 25 in the alignment table 30. When retracted, pin 24 remains below the surface of table 30. In order to advance cant 10 along table 30, certain selected pins 24 are raised and rods 23 are advanced to the right. By using two preselected pins 24 and advancing them by incrementally different lengths, the orientation of cant 10 can be adjusted as it is advanced over the infeed arms 31 and on to saw table 40. After sawing cant 10 into individual boards 10' using saw 41, the outfeed arms 51 lift the boards from sawing table 41 and transfer them onto outfeed conveyor 60. Boards 10' are taken from outfeed conveyer 60 for further processing.
Automatic sawing systems of earlier art required that, after initial alignment, the cant be translated axially under one or more stationary saws. It will be appreciated that it is generally difficult to maintain the alignment of the cant while it is being advanced beneath the saws. The need to advance the cant inhibits the ability to firmly hold the board in the preselected orientation. McGeehee proposes instead to hold the cant fixed on a table and cut it by means of moving saw blades 41 and in the direction 42, as shown in FIGS. 1a and 1b. Nevertheless, the alignment that is performed by using chains and alignment pins is complicated.
It is instructive to also mention another prior art method where positive alignment is secured by first removing an edge of a cant by an overhead saw. Thereafter, the cant is advanced beneath overhead saws with the sawn edge held against a fixed side wall or fence. In this way, the alignment of the cant beneath the saws is improved, although after sawing the leading edge off, internal stress release can cause the "straight" edge to buckle resulting in misalignment. Further, if the cant is being cut by gang rip saws, there is no easy method to select different saw patterns--the only saw pattern used will be the one starting at the fence edge.
Infeed systems are generally one-sided, that is, wood stock is fed into the gang saw from one side only. There are some infeed systems of more recent vintage which employ two sides for feeding cants for the purposes of achieving higher yield and productivity. In U.S. Pat. No. 5,381,712 (Head), for example, the cants are supplied to loading stations arranged on opposite sides of the feeding station, whereupon prior to lateral transport to the feeding station, a cant at either of the loading stations is selectively oriented by the operator relative to a reference line parallel with the longitudinal infeed axis of the saw means, thereby to effect maximum yield from the cant. In taking advantage of the two-sided infeed system, however, a complex pivoting skewing tube and transport is introduced to obtain proper alignment of the cant. Additionally, a clamp is provided with the laterally shiftable skewing tube between loading stations for fixing the cant in a particular orientation for the sawing operation.
The present invention has been developed to provide an novel approach to the optimizing and automated feeding of fixed arbor gang rip saws without the complications associated with prior art apparatus and methods. The disclosed apparatus together with its new method of application bring much needed improvements to wood cutting operations, as discussed more in detail below.